Circuit arrangement capable of continuously varying tone colors for electrical musical instruments

ABSTRACT

A circuit arrangement connected between tone signal generators and a loud-speaker so as to continuously vary tone colors by successively changing the relatively narrow frequency bands of tone signals transmitted from the tone generators to the loud speaker over a relatively broad frequency range of tone signals. There are supplied tone signals to a variable gain amplifier having a feedback reactive impedance element disposed between the output and input with the magnitude of a reactive input impedance controlled by the Miller effect. To constitute a resonance circuit or filter jointly with the feedback reactive input impedance of the amplifier there is connected to the input terminal of the variable gain amplifier a fixed reactive impedance element or a feedback reactive impedance element associated with another variable gain amplifier. The variable gain amplifier has its gain continuously and reciprocally controlled by a potentiometer or photoconductive element which is controlled by a pedal operated with player&#39;&#39;s foot, thereby continuously varying the frequency band of tone signals transmitted from the tone signal generators to the loud-speaker to obtain the so-called wow-wow effect.

United States Patent 1 Niinomi [75] Inventor: NaoyukiNiinomiflamamatsu,

Japan I 73 l Assignee: Nippon Gakki Seizo Kabushiki Kaisha,Hamamatsu-shi J apan 22 Filed; oci.4',1971 211 Appl.No.:186,25S

[30] Foreign Application Priority Data Oct. 5, 1970 Japan 45/86915 Oct.5, 1970 Japan..' 45/98536 [52] US. Cl 84/114, 84/1.11, 84/119 [51] Int.Cl. Gl0h 1/02 [58] Field of Search 84/l.0l, 1.11, 1.19, 84/124, DIG. 10,1.09, 1.1, 1.12,1.21, 1.27, 366, 444

[5 6] References Cited UNITED STATES PATENTS 2,986,953 6/1961 De Armondet al 84/].27 X 3,530,224 9/1970 Plankett et al 84/1 11 3,519,720 7/1970Banger 84/124 X 3,569,603 3/1971 Kern .....84/l.19 3,604,829 9/1971Bunger 84/].19 3,255,296 6/1966 Peterson 84/124 1 July 31, 1973 PrimaryExaminerRichard B. Wilkinson Assistant Examiner-Stanley J. WitkowskiAttorney-Solon B. Kemon et a1.

[5 7] ABSTRACT A circuit arrangement connected between tone signalgenerators and a loud-speaker so as to continuously vary tone colors bysuccessively changing the relatively I 1 narrow frequency, bands of tonesignals transmitted I from the tone generators to the loud speaker overa'relatively broad frequency range of tone signals. There are suppliedtone signals to a variable gain amplifier having a feedback reactiveimpedance element disposed between the output and input with themagnitude of a reactive input impedance controlled by the Miller effect.To constitute a resonance circuit or filter jointly withthe feedbackreactive input impedance of the amplifier there is connected to theinputterminal of the variable gain amplifier a fixed reactive impedanceelement or a feedback reactive impedance element associated with anothervariable gain amplifier. The variable gain amplifier has its gaincontinuously and reciprocally controlled by a potentiometer orphotoconductive element which is controlled by a pedal operated withplayers foot, thereby continuously varying the frequency band of tonesignals transmitted from the tone signal generators to the loud-speakerto obtain the so-called wow-wow effect.

4 Claims, 13 Drawing Figures OUTPUT 47k P'AIIzIIIaII w I 3.749.909

SHEEI 1 0F 5 wow-wow 1 F I G. 1 CIRCUIT g H PESIISSRING 7 agle: lgygFILTER E 9 EST 4O CONII'ROL l KEYBOARDS .HE8R S g FILTER EW 4b I l TONEcoLoRING FILTER E in INPUT I e I 7 wow wow Q cIRcdIT F l G. 3 F l G. 4

I OUTPUT.

I V L Cin Ion PAIENIEUJIVIIQ 1 1111.1

SHEET 2 [IF 5 FREQUENCY (HZ) ll m8 .SnEbO FIG.7

Ill Ambv FDQhDO FREQUENCY (HZ) PAIENTEDJULSI 191a SHEET 3 0F 5 A 5GZMSSE 000m 009 00m 0009 000m 00m 00? Om PATENTEU v 3. 749.809

saw u [If 5 55k 47k 5.6K

OUTPUT dB FREQUENCY (HZ) CIRCUIT ARRANGEMENT CAPABLE OF CONTINUOUSLYVARYING TONE COLORS FOR ELECTRICAL MUSICAL INSTRUMENTS BACKGROUND OF THEINVENTION This invention relates to electrical or electronic musicalinstruments and more particularly to a circuit arrangement enabling aplayer to vary tone colors continuously by a simple operation duringperformance on such instrument.

In an electrical musical instrument, for example, an electronic organ,there are supplied tone signals from tone generators to tone coloringfilters selectively by keyboard operation to be converted to musicaltone signals having tone colors like those of, for example, flutes, orstring instruments. In this case, such musical tone signals may befurther modulated in amplitude or frequency so as to obtain variousmusical effects. However, the formation of such tone colors or thegeneration of musical effects is carried out entirely by operation ofpredetermined switches, making it impossible for a player to vary tonecolors continuously as he desires during performance, namely,,to obtainthe socalled wow-wow effect.

The wow-wow effect is attained by picking up only tone signals having arelatively narrow frequency band from among those having a relativelybroad frequency band and continuously shifting the picked up narrow bandover the entire predetermined frequency range. Such wow-wow effect iffavorably applied to not only electronic organs but also otherelectrical musical instruments such as an electric guitar.

SUMMARY OF THE INVENTION It is accordingly the object of this inventionto provide a circuit arrangement adapted for use with electronic orother electrical musical instruments which is capable of reliablyrealizing the wow-wow effect.

According to this invention, a circuit for generating the wow-woweffect'is connected between tone signal generators and loud-speaker. Inan embodiment of the invention, the wow-wow effect circuit includes avariable gain amplifier impressed with tone signals and a feedbackreactive impedance element connected between the output and input of theamplifier. The reactive input impedance of the amplifier varies with theMiller effect, that is, the magnitude of a gain obtained bytheamplifier. When, therefore, there is connected to the input of theamplifier a reactive impedance element constituting a resonance circuitor filter with the feedback reactive impedance element, then thefrequency band of tone signals to be transmitted from the tone signalgenerators to the loudspeaker varies with the magnitude of gain of thevariable gain amplifier. The gain of the amplifier is adjusted bycontrolling A.C. impedance circuit connected to the input of theamplifier. Control of the A.C. impedance can be continuously carried outby a pedal operable with a players foot, simplifying the attainment ofthe wow-wow effect.

In another embodiment of the invention, there are provided two parallelvariable gain amplifiers which have corresponding feedback reactiveimpedance elements jointly constituting a resonance 'CIICUII.TI16Samplifiers are so designed that when one of them has a large gain, theother presents a small gain. According'ly, the magnitudes of theapparent reactive input impedance of the amplifiers vary in thesamedirection,

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of anelectronic organ system utilizing this invention;

FIG. 2 is a block diagram of a wow-wow effect impartingamplifieflloudspeaker system according to the invention;

FIG. 3 represents the arrangement of a wow-wow cir- 3' cuit according toan embodiment of the invention;

FIG. 4 is an equivalent circuit diagram to that of FIG.

FIG. 5 is a characteristic diagram showing the properties of the circuitof FIG. 3;

FIG. 6 is a modification of FIG. 3;

FIG. 7 shows a characteristic diagram of the properties of thecircuit ofFIG. 6;

FIG. 8 represents the arrangement of a wow-wow circuit accordingtoanother embodiment ofthe invention;

FIG. 9 is a characteristic diagram showing the properties of the circuitof FIG. 8; FIG. 10 indicates the arrangement of a wow-wow circuitaccording to still another embodiment of the invention,

FIG. I] is a characteristic diagram illustrating the properties of thecircuit of FIG. 10;

FIG. 12 is a schematic sectional view of an expression I pedal used toobtain the wow-wow effect; and

DESCRIPTION OF THE PREFEERED EMBODIMENTS FIG. 1 is a block diagram of anelectronic organ system including an wow-wow circuit. Tone signals witha relatively broad frequency band produced by tone generators l areselectively conducted by operation of keyboards 3 through tone keyers 2to tone coloring filters 4a to 4n to be converted to musical tonesignals. Outputs of the filters4a to 4n are connected to a loudspeaker 7through an expression control 5 and amplifier 6. The expression-control5 is, as is well known, controlled by the pedal 8 of an electronic organto change sound volumes.

There has been roughly outlined the arrangement of the known electronicorgan system. According to the present invention, there is furtherprovided a wow-wow circuit 9 between the tone keyrs 2 and expressioncontrol 5. Output of the wow-wow circuit is connected to the expressioncontrol 5 through avariable resistor 10. When there is not required-toproduce the ,wow-wow effect, the variable resistor 10 has only to be soadjusted as to obtain no output from the wow-wow circuit means Sdirectly or through the wow-wow circuit 9. Output of the amplifier 6 isconnected to the loudspeaker 7. In this case, too, the wow-wow circuit 9may be controlled by the pedal means operable by players foot.

Also in an electronic organ, the wow-wow circuit may be inserted betweenthe output side of the tone coloring filters and the input side of theexpression control, in an selectively connectable manner as in FIG. 2.

FIG. 3 illustrates the arrangement of the wow-wow circuit 9 according toan embodiment of this invention. Tone signals supplied to the inputterminal 11 are amplified by a transistor 12, the emitter output ofwhich is coupled to the base of a transistor 13. The collector output ofthe latter transistor 13 is connected to the output terminal 14 of thewow-wow circuit 9 through a coupling capacitor 15. The collector outputof transistor 13 is coupled to the base of another transistor 16 throughresistors 17 and 18. The emitter output of transistor 16 is connected tothe base of the aforesaid transistor 13 through a feedback impedanceelement or capacitor 19. There is conected a choke coil between point xon a signal passage extending from the emitter of transistor 12 to thebase of transistor 13 and a predetermined referential potential point.Between the junction of resistors 17 and 18 and the power voltage line(A.C. ground) are connected in series a capacitor 21 and aphotoconductive element 22 whose resistance varies with the amount oflight projected thereon, thereby constituting a variable A.C. impedancecircuit.

The photoconductive element 22 is controlled, as later described, bypedal means operable by players foot to have its resistance continuouslyvaried. The resultant change in the A.C. input impedance of thetransistor amplifier l6 enables it to act as a variable gain amplifier.

The feedback capacitor 19 renders the apparent input impedance of theamplifier 13 capacitive. The input capacitance Cin of the inputimpedance may be expressed by the following equation based on the wellknown Miller effect.

where:

C actual capacitance of the feedback capacitor 19 A, gain of theamplifier 13 A gain of the amplifier 16 Since the gain A of theamplifier 16 is variable as previously described, the input capacitanceCin is also variable. Accordingly, the choke coil 20 with an inductanceL connected to the input of the amplifier 13 and the input capacitanceCin of the amplifier l3 jointly constitute, as shown in FIG. 4, parallelresonance circuit having a resonance frequencyfof lz'n' y/LCin.

Since Cin is variable, the resonance frequency f is also variable. Ascan be easily understood, the forego ing arrangement may be deemed asequivalent to the connection of the resonance circuit having frequencyselectivity beween the input terminal 11 and output terminal 14 of thewow-wow circuit 9. The frequency band of tone signals transmitted fromthe input terminal 11 to the output terminal 14 of the wow-wow circuit 9varies, as illustrated in FIG. 5, according to the resistance of thephotoconductive element 22.

Referring to FIG. 5, the curve a represents the property of the wow-wowcircuit 9 when the photoconductive element 22 had a resistance of 470kiloohms, and

the curves b, c and d denote those obtained with resistances of 47kiloohms, 4.7 kiloohms and 470 ohms respectively.

- As apparent from FIG. 5, the wow-wow circuit of FIG. 3 picks up onlytone signals having a relatively narrow frequency band from among thosehaving a relatively broad frequency band and conducts them to the outputterminal 14 thereof. The frequency band of the former tone signalsis'continuously shifted over a relatively broad frequency range underthe control of the variable gain amplifier 16, thereby providing thewowwow effect.

In FIG. 3, the choke coil 20 and input capacitance Cin jointlyconstituted a resonance circuit by being disposed in parallel with eachother. As shown in FIG. 6, however, they may form a low pass filter. Tothis end, the choke coil 20 is connected between the output of theamplifier 12 and the input of the amplifier 13. In this case, there isprovided a low pass filter assuming an inverted L shape.

FIG. 7 shows the characteristics of the wow-wow circuit of FIG. 6. Thecurve a denotes theproperty of the wow-wow circuit when. thephotoconductive element 22 had a resistance of 470 kiloohms and thecurve b that obtained with the resistance of 470 ohms.

Control of the photoconductive element 22 can be conveniently effectedby the horizontal operation of the expression pedal 8 which controls thevolumes of sounds by its vertical movement as illustrated in FIG. 1.There will .be later described the mechanism by which the expressionpedal 8 is made to move in a horizontal plane.

In the foregoing embodiment, one of the two reactive impedance elementsjointly constituting a resonance circuit was rendered variable. However,it is possible to make both reactive impedance elements variable so asto broaden the range of varying resonance frequency.

There will now be described the latter case by reference to FIG. 8.Input signals are supplied to the base of the transistor amplifier 12through the input terminal 11. The emitter output of the transistoramplifier 12 is coupled to the base of the transistor amplifier 13. Thecollector output of the latter amplifier 13 is connected to the outputterminal 14 through another transistor amplifier 30. The collectoroutput of the transistor 13 is connected to the base of a first stagetransistor 32, a component of a two-stage amplifier 31. The emitteroutput of the first stage transistor 32 is connected to the base of asecond stage transistor 33. Between the emitter of transistor 33 and thebase of transistor 13 is connected to the feedback capaciton 19. Theemitter output of the first stage transistor 32 forming part of theaforesaid first two-stage amplifier 31 is connected to the base of afirst stage transistor 36, a component of a second two-stage amplifier35through a transistor 34. The emitter output of the transistor 36 isconnected to the base of a second stage transistor 37 forming part ofthe second two-stage amplifier 35. Between the emitter of transistor 37and the base of transistor 13 is connected the feedback inductor 20. Thecollector output of the transistor 13 is coupled to the base of thefirst stage transistor 36 included in the second two-stage amplifier 35.Between the base of the first stage transistor 32 included in the firsttwo-stage amplifier 31 and the power voltage line is connected avariable A.C. impedance circuit consisting of the capacitor 21 andphotoconductive element 22. As in the preceding embodiment, control ofthe intensity of light projected on the photoconductive element 22converts the first twostage amplifier 31 to a variable gain amplifier.

Referring to the second two-stage amplifier 35, the base of thetransistor 36 is supplied with output from the collector of thetransistor 13 and output from the collector of the transistor 34. Thelatter output is controlled in level by the variable gain amplifier 31and has its phase inverted from the output of the transistor 13 by thetransistor 34 itself. Accordingly, when the variable gain amplifier 31has a large gain, input signals to the second two-stage amplifier 35decrease in level, or

vice versa. Namely, the second two-stage amplifier 351 is controlled bythe gain of .the variable gain amplifier The inductor 20 connectedbetween the output of the variable amplifier 35 and the input of theamplifier 13 provides apparent inductive input impedance to theamplifier 13. The apparent inductance Lin may be indicated by thefollowing equation.

Lin L/(1+A,-A

where:

L actual inductance of the inductor 20 A gain of the second two-stagevariable gain amplifier 35 of the other; said Since the gain A of theamplifier 13 is fixed, the small gain A of the amplifier 31 decreasesCin and the large gain A of the amplifier 35 reduces Lin. The resonancefrequency fobtained by Cin and Lin may be expressed by the followingequation:

f= Arr 1/Lin-Cin I The gain A of the first variable gain amplifier 31and the gain A of the second variable gain amplifier 35 vary in oppositedirections, causing the capacitance Cin and the inductance Lin to changein the same direction. Thus. the resonance frequency can be broadlyvaried in succession by continuously changing the resistance of thephotoconductive element 22. FIG. 9 represents variation in the resonancefrequency.

There will now be described by reference to FIG. 10 a wow-wow circuitaccording to still another embodiment of this invention. The collectoroutput of the transistor 13 is connected to the inputs of the first andsecond two-stage amplifilers 31 and 35. Output of the first amplifier 31is connected to the input of the transistor 13 through the feedbackcapacitor 19. Output of the second amplifier 35 is connected to theinput of the transistor 13 through the feedback inductor 20. Between theinputs of the first and second amplifiers 31 and 35 is connected apotentiometer 40 provided with a slidable arm 41, which is connected tothe power voltage line through a capacitor 42.

When, in FIG. 10, the slidable arm 41 lies at the uppermost part of thepotentiometer 40, the A.C. input impedance of the first amplifier 31 ismost reduced with the resultant smallest gain. At this time the secondamplifier 35 has the largest A.C. input impedance, that is, a maximumgain. Conversely, when the slidable arm 41 is brought to the lowermostpart of the potentiometer 40, the first amplifier 31 has the largestgain and the second amplifier 35 the smallest gain. Obviously,therefore, control of the slidable arm 41 enables the gain of the firstamplifier 31 and that of the second amplifier 35 to vary in oppositedirections. Thus the wowwow circuit of FIG. 10 acts in the same way asthat of FIG. 8.

FIG. 11 represents the characteristics of the wowwow circuit of FIG. 10.The curve a shows the characteristics of the circuit when the slidablearm 41 lies at the lowermost part 'ofthe variable resistor 40, and thecurve b those which appear when the arm 41 stands at the uppermost partof the resistor 40.

i There will now be described by reference to FIGS. 12 and 13 theexpression pedal adapted for use with an electronic organ to obtain thewow-wow effect. To a stand 51 is fitted a first base plate 50 so as torotate vertically by means of a horizontal shaft 52. The expression ofan electronic organ is controlled by the vertical rotation of the baseplate 50 resulting from the operation of players foot. To simplifythe-drawing ofv FIG. 12, there are omitted the known mechanical andelectrical means for controlling the expression by the aforesaidvertical movement of the base plate 50. Above the base plate 50 isdisposed a second base plate 53 through a slidable spacer made of, forexample, poly ethylene. To the underside of the substantially centralpart of the second base plate 53 is fitted a vertical shaft 55 so as topenetrate the first base plate 50. Numeral 56 represents a bearing madeof synthetic resin for the vertical shaft 55,57 a rubber ring having aspring action, 58 a washer and 59 a nut. Thus the second base plate 53can rotate about the vertical shaft 55 in a horizontal plane, namely,vertically as viewed from the surface of the drawing paper. The secondbase plate 53 may be covered with a rubber cover 60 and a rubber plate61 provided with a plurality of grooves, so as to be rotated in ahorizontal plane simply by the operation of players foot.

On the underside of the forward end of the first base plate 50 arespatially disposed a light source section 62 and a light receivingsection 63. The light receiving section 63 includes a photoconductiveelement 64 and a plate 65 positioned ahead thereof which is perforatedwith a slit 66 shown in FIG. 13. Further to the underside of the forwardend of the second base plate 53 is fitted a plate 67 which is insertedbetween the light source section 62 and the light receiving section 63and is bored with, for example, a triangular slit 68 illustrated in FIG.13. It will be apparent, therefore, that the rotation of the second baseplate 53 in a horizontal plane around the shaft 55 enables the lightfrom the light source section 62 to be projected on the photo conductiveelement 64 through the triangular slit 68 of the plate 67 in varyingintensity.

In the case of an electric guitar, the vertical rotation of the pedalcan produce a wow-wow effect. In the case of an electronic organ, thewow-wow effect can be obtained by the operation ofa knee lever, in placeof the pedal means. i

What is claimed is: 1. An electrical musical instrument comprising:means for generating tone signals having a'relatively broad frequencyband;

loud-speaker means for converting said tone signals to audible sounds;

circuit means connected between said tone signal generating means andloud-speaker means to pick up only tone signals having a relativelynarrow frequency band from among those having said relatively broadfrequency band and transmit the former tone Signals from said tonesignal generating means to said loud-speaker means, said circuit meansincluding a variable gain amplifier whose gain varies in accordance withthe magnitude of an A. C. inputimpedance, and a reactive impedanceelement connected between the output. and input of said amplifier toprovide an apparent reactive impedance to said amplifier according tothe magnitude of its gain; a foot operated pedal movable in a horizontalplane; means in the gain circuit of said amplifier and connected to saidfoot operated pedal for continuously controlling the gain of saidamplifier in response to horizontal movement of said pedal therebysuccessively to shift the relatively narrow frequency band of tonesignals transmitted from said tone generating means to said loud speakermeans over said relatively broad frequency range of tone signals;

said circuit means further including first amplifier means foramplifying tone signals; second amplifier means connected to the outputof said first amplifier means; third amplifier means connected to theoutput of said first amplifier means; a variable A.C. impedance circuitconnected to the inputsf said second and third amplifier means andcontrolled by said gain varying means to cause either of the second andthird amplifier means to have a larger gain than theother; a firstreactive impedance means connected between the output of said secondamplifier means and the input of sai first amplifier means to providesaid first and second amplifier means with a first apparent reactiveinput impedance whose magnitude varies with the gain of said secondamplifier means; and a second reactive impedance means connected betweenthe output of said third amplifier means and the input of said firstamplifier means to provide said first and third amplifier means with asecond apparent reactive input impedance whose magnitude varies with thegain of said third amplifier means and constitute a resonance circuitwith said first apparent reactive input impedance.

2. An electrical musical instrument according to claim 14 wherein saidA.C. impedance circuit includes a potentiometer provided with a slidablearm and connected between the input terminals of said second and thirdamplifier means and a capacitor connected between said slidable arm andan A.C. grounded point.

3. An electrical musical insturment comprising:

means for generating tone signals having a relatively broad frequencyband;

loud-speaker means for converting said tone signals to audible sounds;

circuit means connected between said tone signal generating means andloud-speaker means to pick up only tone signals having a relativelynarrow frequency band from among those having said relatively broadfrequency band and transmit the former tone signals from said tonesignal generating means to said loud-speaker means, said circuit meansincluding a variable gain amplifier whose gain varies in accordance withthe magnitude of an A.C. input impedance, and a reactive impedanceelement connected between the output and input of said amplifier toprovide an apparent reactive impedance to said amplifier according tothe magnitude of its gain; g a foot operated pedal movable in ahorizontal plane; means in the gain circuit of said amplifier andconnected to said foot operated pedal for continuously controlling thegain of said amplifier in response to orizontal movement of said pedalthereby successively to shift the relatively narrow frequency band oftone signals transmitted from said tone generating means to saidloud-speaker means over said relatively broad frequency range of tonesignals; said circuit means further including; first amplifier means foramplifying tone signals; second amplifier means connected to the outputof said first amplifier means; a variable A.C. impedance circuitconnected to the input of said second amplfier means to be controlled bysaid gain varying means so as to vary the gain of said second amplifiermeans; means for drawing out output from said second amplifier meanswhose phase is reversed from that of output of said first amplifiermeans; third amplifier means connected to the output of said firstamplifier means and said means for drawing out .output whose phase isreversed from that of output of said first amplifier means to have thegain of said third amplifier means itself varied apparently in reverserelationship from said second amplifier means; a first reactiveimpedance means connected between the output of said second amplifiermeans and the input of said first amplifier means to provide said firstand second amplifier means with the first apparent reactive inputimpedance whose magnitude varies with the gain of said second amplifiermeans; and a second reactive impedance means connected between theoutput 'of said third amplifier means and the input of said firstamplifier means so as to supply said first and third amplifier meanswith the second apparent reactive input impedance whose magnitude varieswith the gain of said third amplifier means and constitute a resonancecircuit jointly with the first reactive impedance. 4. An electricalmusical instrument according to claim 3 wherein said A.C, impedancecircuit includes a series connection of a capacitor and a variableresistor, said capacitor being connected between the input terminal ofsaid second amplifier means and an A.C. ground point, and said variableresistor being a photoconductive element whose resistance varies withthe intensity of light projected thereon.

ill I?

1. An electrical musical instrument comprising: means for generatingtone signals having a relatively broad frequency band; loud-speakermeans for converting said tone signals to audible sounds; circuit meansconnected between said tone signal generating means and loud-speakermeans to pick up only tone signals having a relatively narrow frequencyband from among those having said relatively broad frequency band andtransmit the former tone signals from said tone signal generating meansto said loud-speaker means, said circuit means including a variable gainamplifier whose gain varies in accordance with the magnitude of an A. C.input impedance, and a reactive impedance element connected between theoutput and input of said amplifier to provide an apparent reactiveimpedance to said amplifier according to the magnitude of its gain; afoot operated pedal movable in a horizontal plane; means in the gaincircuit of said amplifier and connected to said foot operated pedal forcontinuously controlling the gain of said amplifier in response tohorizontal movement of said pedal thereby successively to shift therelatively narrow frequency band of tone signals transmitted from saidtone generating means to said loud speaker means over said relativelybroad frequency range of tone signals; said circuit means furtherincluding first amplifier means for amplifying tone signals; secondamplifier means connected to the output of said first amplifier means;third amplifier means connected to the output of said first amplifiermeans; a variable A.C. impedance circuit connected to the inputs f saidsecond and third amplifier means and controlled by said gain varyingmeans to cause either of the second and third amplifier means to have alarger gain than theother; a first reactive impedance means connectedbetween the output of said second amplifier means and the input of saifirst amplifier means to provide said first and second amplifier Meanswith a first apparent reactive input impedance whose magnitude varieswith the gain of said second amplifier means; and a second reactiveimpedance means connected between the output of said third amplifiermeans and the input of said first amplifier means to provide said firstand third amplifier means with a second apparent reactive inputimpedance whose magnitude varies with the gain of said third amplifiermeans and constitute a resonance circuit with said first apparentreactive input impedance.
 2. An electrical musical instrument accordingto claim 14 wherein said A.C. impedance circuit includes a potentiometerprovided with a slidable arm and connected between the input terminalsof said second and third amplifier means and a capacitor connectedbetween said slidable arm and an A.C. grounded point.
 3. An electricalmusical insturment comprising: means for generating tone signals havinga relatively broad frequency band; loud-speaker means for convertingsaid tone signals to audible sounds; circuit means connected betweensaid tone signal generating means and loud-speaker means to pick up onlytone signals having a relatively narrow frequency band from among thosehaving said relatively broad frequency band and transmit the former tonesignals from said tone signal generating means to said loud-speakermeans, said circuit means including a variable gain amplifier whose gainvaries in accordance with the magnitude of an A.C. input impedance, anda reactive impedance element connected between the output and input ofsaid amplifier to provide an apparent reactive impedance to saidamplifier according to the magnitude of its gain; a foot operated pedalmovable in a horizontal plane; means in the gain circuit of saidamplifier and connected to said foot operated pedal for continuouslycontrolling the gain of said amplifier in response to orizontal movementof said pedal thereby successively to shift the relatively narrowfrequency band of tone signals transmitted from said tone generatingmeans to said loud-speaker means over said relatively broad frequencyrange of tone signals; said circuit means further including; firstamplifier means for amplifying tone signals; second amplifier meansconnected to the output of said first amplifier means; a variable A.C.impedance circuit connected to the input of said second amplfier meansto be controlled by said gain varying means so as to vary the gain ofsaid second amplifier means; means for drawing out output from saidsecond amplifier means whose phase is reversed from that of output ofsaid first amplifier means; third amplifier means connected to theoutput of said first amplifier means and said means for drawing outoutput whose phase is reversed from that of output of said firstamplifier means to have the gain of said third amplifier means itselfvaried apparently in reverse relationship from said second amplifiermeans; a first reactive impedance means connected between the output ofsaid second amplifier means and the input of said first amplifier meansto provide said first and second amplifier means with the first apparentreactive input impedance whose magnitude varies with the gain of saidsecond amplifier means; and a second reactive impedance means connectedbetween the output of said third amplifier means and the input of saidfirst amplifier means so as to supply said first and third amplifiermeans with the second apparent reactive input impedance whose magnitudevaries with the gain of said third amplifier means and constitute aresonance circuit jointly with the first reactive impedance.
 4. Anelectrical musical instrument according to claim 3 wherein said A.C.impedance circuit includes a series connection of a capacitor and avariable resistor, said capacitor being connected between the inputterminal of said second amplifier means and an A.C. ground point, andsaid variable resistor being a photoconductive element whose resistancevaries with the inteNsity of light projected thereon.